Develop Reference

I want to make universal method in CLASS for all enums

public class TableContent {
public static String EXCEL_SHEET_NAME = Nit.THEAD.getName();
public static String FILENAME= Nit.FILENAME.getName();
public enum Nit {
FILENAME("Nit-workorder-list"),
THEAD("NIT WORKORDER"),
TENDERSPECNO("TENDER SPECFICATION NO."),
FEE("TENDER FEE"),
SDAMOUNT("SD AMOUNT"),
TYPE("NIT TYPE"),
PRE_BID("PRE BIDDING DATE"),
OPEN_DATE("OPENING DATE"),
STATUS("CONTRACTOR STATUS");
private final String name;
public String getName() {
return name;
}
private Nit(String name) {
this.name = name;
}
public static Nit getNitHeadByName(String name)
{
Nit[] nit=Nit.values();
if(nit==null)
{
return null;
}
for(Nit nitHead:nit)
{
if(nitHead.getName().equals(name))
return nitHead;
}
return null;
}
public enum NitWorkOrder {
}
public enum NitList {
}
My objective is:
I want to export excel sheet from my application, every time I need to hardcode the table headings, which was not good programming practice.
So I use enum to overcome the hardcode problem. Now there are different table heading according to the list, then I enclosed all the required ENUMS in single class.
I used to write getXXXByName() and getXXXByValue() to access the enum, by name or by value.
But he problem is I need to write getXXXByName() and getXXXByValue() everytime inside each enum. I want to write these methods inside the class and outside the enums, and access those methods with the help of class name.
I just want to declare my constants inside enum.
Please kindly suggest me an idea or a way so I can make this method universal which will work for each and every enum. I want to write these methods in such a way so it can be accessed for all enums enclosed in my class. I thought about generics but I have little knowledge.

You can use generics to push functionality up to a parent class by telling the parent class that the type is an enum that implements an interface.
// Use an interface to inform the super class what the enums can do.
public interface Named {
public String getName();
}
// Super class of all Tables.
public static class Table<E extends Enum<E> & Named> {
private final Class<E> itsClass;
private final String sheetName;
private final String fileName;
public Table(Class<E> itsClass) {
this.itsClass = itsClass;
// Walk the enum to get filename and sheet name.
String sheetName = null;
String fileName = null;
for ( E e: itsClass.getEnumConstants() ){
if ( e.name().equals("FILENAME")) {
fileName = e.getName();
}
if ( e.name().equals("THEAD")) {
sheetName = e.getName();
}
}
this.sheetName = sheetName;
this.fileName = fileName;
}
// Use the interface and the enum details to do your stuff.
public E getByName (String name) {
for ( E e: itsClass.getEnumConstants() ){
if ( e.getName().equals(name)) {
return e;
}
}
return null;
}
}
// Extend Table and tell it about your enum using the super constructor.
public static class TableContent extends Table<TableContent.Nit> {
public TableContent() {
super(TableContent.Nit.class);
}
public enum Nit implements Named{
FILENAME("Nit-workorder-list"),
THEAD("NIT WORKORDER"),
TENDERSPECNO("TENDER SPECFICATION NO."),
FEE("TENDER FEE"),
SDAMOUNT("SD AMOUNT"),
TYPE("NIT TYPE"),
PRE_BID("PRE BIDDING DATE"),
OPEN_DATE("OPENING DATE"),
STATUS("CONTRACTOR STATUS");
private final String name;
Nit(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
}

Interface Segregation Principle

I'm learning SOLID principles with Java and I'm trying to implement two classes with this. My problem is about ISP. I have some methods that is present in one class but not in the other and I also have to refer both classes with the same interface.
This is the first class:
public final class Complex implements Number {
#Override
public String polarForm() {
//This class needs to implement this method
}
#Override
public String rectangularForm() {
//This class needs to implement this method
}
}
Here is the second one:
public final class Real implements Number {
#Override
public String polarForm() {
//This class does not need this method!
}
#Override
public String rectangularForm() {
//This class does not need this method!
}
}
Finally I have to refer to the classes something like this:
public static void main(String[] args) {
Number c = new Complex();
Number r = new Real();
Number n = c.add(r);
System.out.println(c.polarForm());
System.out.println(n);
}
How can I refer to both classes with the same interface without implementing unnecessary methods?

An alternate solution to approach this problem would be to use Composition instead of Inhertiance in conjunction to the interface segregation principle.
Number class
public class Number {
private RectangleForm rectangleForm;
private PolarForm polarForm;
private BigDecimal value;
public Number(RectangleForm rectangleForm, PolarForm polarForm,BigDecimal value) {
this.rectangleForm = rectangleForm;
this.polarForm = polarForm;
this.value = value;
}
public String polarForm() {
return polarForm.transform(this.value);
}
public String rectangleForm() {
return rectangleForm.transform(this.value);
}
//other methods such as add and subtract
}
PolarForm interface
public interface PolarForm {
public String transform(BigDecimal number);
}
RectangularForm interface
public interface RectangleForm {
public String transform(BigDecimal number);
}
RectangleForm implementation for real numbers
public class RectangleFormReal implements RectangleForm {
#Override
public String transform(BigDecimal number) {
String transformed = "";
//transfromed = logic to transform to rectangle form
return transformed;
}
}
PolarForm implementation for Real numbers
public class PolarFormReal implements PolarForm {
#Override
public String transform(BigDecimal number) {
//return the number as is without any transformation
return number.toString();
}
}
Putting the pieces together
public class NumberTest {
public static void main(String[] args) {
RectangleForm rf = new RectangleFormReal();
PolarForm pf = new PolarFormReal();
Number number = new Number(rf, pf,new BigDecimal(10));
String rectangleForm = number.rectangleForm();
String polarForm = number.polarForm();
}
}
You can create the PolarFormComplex and RectangleFormComplex implementations and wire theNumber instance in a similar fashion. The advantage of this approach is that your code will always rely on the interface of the Number class (by interface I mean the public APIs) and you can chose the transformation strategy by injecting the corresponding PolarForm or RectangleForm instances into your Number instance at compile time as shown above or at runtime (via a factory)

Break your Number interface (or base class) into multiple interfaces. The standard operations (add, subtract, etc) are in one; let's say INumber. polarForm and rectangularForm are part of another; let's say IComplex.
Real would implement INumber; Complex would implement INumber and Icomplex. You could then treat both as INumber.
If necessary, you could also create another interface that implements both.

I am trying to implement OOP concepts with java

When i try to compile an aggregation program , i receive an error saying "class,interface,enum expected". Here is my code. please help me solve this issue.
class employee
{
private String name;
private String address;
private float salary;
public employee(String na, String add,float sal)
{
name = na;
address = add;
salary = sal;
}
public void showEmpDetails()
{
System.out.println("Name " + name);
System.out.println("Address " + address);
System.out.println("Salary " + salary );
System.out.println();
}
}
import java.util.vector;
class company
{
private String comname;
private vector vt;
public company(String na)
{
comname = na;
vt = new vector();
}
public void addEmployee(employee e)
{
vt.addElement(e);
}
public void showComDetails()
{
System.out.println("Company Name " + comname);
int x = vt.size();
int y = 0;
while(y<x)
{
object e = vt.elementAt(y);
e.showEmpDetails();
y++;
}
}
}
public class demo
{
public static void main(String[] args)
{
employee e1 = new employee("Ashan","Kandy",2000.0f);
employee e2 = new employee("Steve","California",2500.0f);
employee e3 = new employee("Elon","South Africa",2500.0f);
company c1 = new company("Apple");
c1.addEmployee(e1);
c1.addEmployee(e2);
c1.addEmployee(e3);
c1.showComDetails();
}
}
Note:- i receive only one error. and also can anybody tell me why can't i have more than one public class in java.

Well, your code has more than one error actually. The reason for your specific error is that import should be at beginning of the file, not in the middle.
And my understanding of why only one public class is allowed for each file is:
It makes things clearer.
By reading the class name and document to this class, you could quickly know what the whole file is used for. If we allow multiple public classes in one file, like C++, then we have to jump inside of the file to understand it.
Notice Java is a strong object-oriented language, i.e. everything in Java is Object. So when importing, you are importing a file. It would be more complicated if one file contains multiple public classes.
It simplify testing.
Each public class could have a main function. And you could run any main function of a file Demo.java simply by java Demo. This is really nice, so that you could write test code, or example of usage in main function to show other contributor how this class should be used.
There have to be other more in-depth reason for single public class in Java. But these are my perspective.

Java Referencing Abstract Classes

I am trying to create a game in Java and within this game I am trying to implement a quest / mission system. I have come up with an idea to do this, but I am not sure how I would reference the quests or even if it would work at all. It works as such:
I have an abstract class which defines all of the variables and has a few simple methods. The file resembles this:
public abstract class Quest {
public String name = null;
public int id;
public abstract int getPrerequisite() {
return this.id-1;
}
}
I then have a few files that set values for these variables like the example below.
public class MyFirstQuest {
name = "A quest";
id = 0;
}
I'm not sure if it is possible but is there any way that I could reference the files like so:
Quest MFQ = new MyFirstQuest();
System.out.println(MFQ.name);
or
Quest[] quests = new Quest[10];
quest[0] = new MyFirstQuest();

just replace
public class MyFirstQuest {
name = "A quest";
id = 0;
}
by
public class MyFirstQuest extends Quest{
public MyFirstQuest(){
name = "A quest";
id = 0;
}
}
and there are some tips :
use private variables and use getters like this public String
getName(){return name;}
remove the abstract of the method getPrerequisite

write java interface

as I declare a table of strings in all java testss and functions , is it possible de declare it once in an interface and to call it anywhere ?
public interface string {
string[] mytab = new string[2];
}
in the java class :
public class Test { }
How can I call the inetrface to say :
if (mytab[1].equals("toto")){}

I guess this is what you are asking about. This should work for you.
public interface MyInterface {
static final String myString = "abc";
}
public class Test {
static void test() {
if (MyInterface.myString.equals("abc")) {
// ...
}
}
}

I believe you can define static objects in an interface.